IB BIO TOPIC 5.1 COMMUNITIES & ECOSYSTEMS

Question 1

Define species

Answer 1

Species: a group of organisms that can interbreed and produce fertile offspring.

Question 2

Define Habitat

Answer 2

Habitat: the environment in which a species normally lives or the location of a living organism.

Question 3

Define Population

Answer 3

Population: a group of organisms of the same species who live in the same area at the same time.

Question 4

Define community

Answer 4

Community: a group of populations living and interacting with each other in an area.

Question 5

Define Ecosystem

Answer 5

Ecosystem: a community and its abiotic environment.

Question 6

Define Ecology

Answer 6

Ecology: the study of relationships between living organisms and between organisms and their environment.

Question 7

Distinguish between autotroph and heterotroph.

Answer 7

Autotroph: an organism that synthesizes its organic molecules from simple inorganic substances.
Heterotroph: an organism that obtains organic molecules from other organisms.

Question 8

Distinguish between consumers, detritivores and saprotrophs:

Answer 8

Consumer: an organism that ingests other organic matter that is living or recently killed.

Detritivore: an organism that ingests non-living organic matter.

Saprotroph: an organism that lives on or in non-living organic matter, secreting digestive enzymes into it and absorbing the products of digestion.

Question 9

Describe what is a food chain

Answer 9

• only real examples should be used from natural ecosystems
• A –> B indicates that A is being eaten by B, i.e., the arrow indicates the direction
of energy flow
• each food chain should include a producer and consumers, but not decomposers
• named organisms should be used, at either species or genus level
• common species names can be used instead of binomial names
• general names such as tree or fish should not be used

Question 10

Give three examples of food chains, each with at least three linkages (four organisms).

Answer 10

1. water lily→moth larvae→roach fish→moorhen
2. planktonic algae→water fleas→water boatman→ roach fish→moorhen
3. filamentous algea→haliplid beetles→dragonfly larvae→moorhen

Question 11

Describe what is meant by a food web.

Answer 11

• the elaborate interconnected relationships within an ecosystem based on feeding
and energy transfer

Question 12

Define trophic level.

Answer 12

• the position that an organism occupies in a food chain or a group of organisms in
a community that occupy the same position in food chains
eg., moth larvae, water fleas and haliplid beetles all occupy trophic level 1 in the above food chains.

Question 13

Deduce the trophic level of organisms in a food chain and a food web.

Answer 13

• place an organism at the level of producer, primary consumer, secondary consumer, and so on (as the terms herbivore and carnivore are not always applicable)

Question 14

What are the rules of food chain constructing ?

Answer 14

• only real examples should be used from natural ecosystems
• A –> B indicates that A is being eaten by B, i.e., the arrow indicates the direction
of energy flow
• each food chain should include a producer and consumers, but not decomposers
• named organisms should be used, at either species or genus level
• common species names can be used instead of binomial names
• general names such as tree or fish should not be used

Question 15

What is the initial energy source for almost all communities.

Answer 15

Light is the initial energy source for almost all communities.

Question 16

Explain the energy flow in a food chain.

Answer 16

• energy losses between trophic levels include:

1. material not consumed
2. material not assimilated (bones, feathers, skin – not eaten)
3. heat loss through cell respiration

Question 17

Are energy transformations 100 % efficient ?

Answer 17

NO. Energy is lost between levels through non-consumed material, not assimilated material, heat loss.

Question 18

Explain reasons for the shape of pyramids of energy.

Answer 18

• energy pyramids illustrate the quantity of energy within the biomass of each trophic level
• only a portion of energy in any level is transferred to the next, commonly being 10-20%
• of the plant biomass consumed by a typical herbivore:
1. 50% is not assimilated: lost as faeces (indigestible cellulose)
2. 35% is assimilated but lost as heat during cellular respiration
3. 15% is consumed and assimilated and incorporated into biomass

Question 19

Explain the role of energy in the ecosystem.

Answer 19

• Earth constantly loses much of its incoming energy as it reflects light and radiates heat to space
• producers consume only about 1% of solar energy available to them into organic matter during photosynthesis; thus, about 99% of solar energy never enters, and thus leaves an ecosystem without ever being converted to the energy contained by organisms

Question 20

Explain why generally, the total energy entering an ecosystem equals the total energy lost to the environment.

Answer 20

1. such an ecosystem would be stable
2. in earlier stages of succession, an ecosystem captures more energy than it
   loses, converting the excess into increasing biomass
3. when an ecosystem is disturbed, it might lose more energy to the
   environment than it gains, decreasing in total biomass

Question 21

Explain the roles of nutrients in an ecosystem :

Answer 21

• Earth does not exchange significant amounts of matter with space
• therefore, the total quantity of matter on Earth is static
• ecosystems recycle their nutrients
1. producers use nutrients in their environment, many of which have been formed by decomposition
2. consumers use the nutrients gained from the organisms they eat
3. decomposers break down nutrients from the organisms they decompose,
making simple compounds in the environment available to producers
• recycling requires energy

Question 22

Give 2 examples of organisms that recycle nutrients

Answer 22

saprotrophic bacteria and fungi (decomposers) recycle nutrients.